1. Field of the Invention
The present invention relates to a transceiver applied to an Ethernet system, and particularly to a transceiver without using a crystal oscillator applied to an Ethernet system.
2. Description of the Prior Art
An Ethernet system is a widely used network, which can allow devices (a host and a link partner) at two opposite terminals of the Ethernet system to transmit/receive data simultaneously and to automatically select proper transmitting/receiving speeds. In the Ethernet system, the host and the link partner must utilize a transmission speed based on a specification of the Ethernet system to transmit/receive data. Taking a 100 MHz transmission speed as an example, speed of Multilevel Transmission 3 (MLT3) transmitted on a media document interface (MDI) line needs to be 125 MHz ±100 ppm. If the frequency of the host and the frequency of the link partner is too different, a receiver of the host may not identify data from the link partner, resulting in a connection not being established between the host and the link partner, or in some cases, packets transmitted between the host and the link partner may be wrong.
To satisfy the 125 MHz ±100 ppm requirement, the Ethernet system usually provides an accurate external reference clock to a phase-locked loop of the receiver of the host, and then the phase-locked loop generates a clock that fits the requirement of the Ethernet system. Generally speaking, the Ethernet system utilizes crystal oscillator devices to generate the accurate external reference clock to the receiver of the host. However, crystal oscillator devices are costly and occupy large areas. Therefore, to the way of designing a receiver without using an external reference clock becomes an important issue for a designer.